1. Field of the Invention
The present invention relates to an optical recording and reproducing apparatus which records data on a recording medium and reproduces recorded data by means of a laser.
2. Description of the Related Art
In recent years, high density of optical disc progresses by short-wavelength of light source and high NA (Numerical Aperture) of objective lens. If recording density will be raised more in future, high line-density and high track-density become important. A PRML (Partial Response Maximum Likelihood) signal processing technique or superresolution technique is effective for high line-density. Further, the superresolution technique is promising in high track-density.
The conventional technique makes one data track correspond to one groove or one land. Further, generation of a tracking error signal and data recording and reproducing are performed based on a push-pull method of detecting imbalance of diffraction light from a groove or land by means of a single light beam. For this reason, there is a problem that the amplitude of the tracking error signal is greatly deteriorated with narrowing of the tracks. As a result, stable tracking control cannot be realized.
It is an object of the present invention to provide an optical data recording and reproducing apparatus which realizes stable tracking control for an optical data recording medium of high track density, for example, an optical disc which narrows a track pitch more than the conventional disc.